The present invention relates to a routing method for use in automatically designing the wiring of printed wiring boards, large scale integrated circuit (LSI) chips or the like.
An example of conventional routing methods used for an automatic wiring design in computer aided design (CAD) systems or the like is disclosed on pages 312 to 326 of the publication titled "Design Automation of Digital Systems, Vol. 1, Theory and Techniques" by M. A. Breuer, published in 1972 by Prentice-Hall, Inc. (Reference 1). In the prior art method, a plurality of connection points (grid cells) are arrayed on a plane on which wiring is to be achieved. A path for connecting two designated connection points, i.e., a wiring path, is expressed by the positions of a series of empty cells (each connectable to all other adjacent empty cells) through which this path passes. These cells can be further defined as obstacle cells, which are prohibited from connection with all other adjacent cells. In such a prior art method, however, only the above-mentioned obstacle cells and empty cells can be defined, so that the density of the wiring pattern achievable on the above-mentioned plane becomes uniform on the whole plane. In other words, the method does not allow a region having a different wiring pattern density to be defined on that plane, as will be described later. As a result, it is difficult to apply this method to the wiring design of wiring boards or the like having a plurality of regions of different wiring pattern desities.
An object of the present invention is, therefore, to provide a routing method free from the above-mentioned disadvantage.